In the medico-technical field, several methods of introducing liquid, with or without solid particles, into the body are already available. Most of these methods are based on the use of a needle or catheter in combination with some pumping device such as syringes or infusion pumps. In most applications, the volume of infused or injected liquid, liquid mixture or suspension is also relatively great relative to the dimensions or inner volume of the insertion system, which results in the influence of the system on the final position of the inserted fluid volume in the body being affected only marginally when withdrawing the insertion system. In most applications, the position of the deposition is also not decisive of the clinical efficiency of the infused substance.
In recent years, the requirements for accuracy of the deposition have increased dramatically in the field of, among other things, tissue implants. An example of fields where the accuracy of the deposition is highly decisive of the clinical result is the implantation of cells for treating Parkinson's disease. Cells which preferably are extracted from a foetus are suspended in a physiological solution, which is inserted to the desired position in the brain. The amount of suspended cells is in the order of 10 .mu.l, which corresponds to the volume in a 10 mm length of the catheter by which the substance is introduced. Problems arise when the catheter system is being withdrawn, since a vacuum is generated which sucks back a great part of the infused amount to a non-desired position, resulting in the fact that the implanted cells cannot develop and contribute to a positive clinical effect.